The invention relates to the spreading of granular materials, in particular sanding or salting materials for the winter treatment of roads, or materials for the construction or the repair of roads.
It relates in particular to apparatus for spreading a granular material of the type comprising a conveyor designed to feed the material from a hopper to a distributor.
Apparatus of this type is already known, designed either to be mounted on or to be towed by a truck or the like. The granular material, which is for example salt, sand, gravel, etc, and which is contained in the hopper, is fed by the conveyor to the distributor. The latter is generally in the form of a disk distributor placed at the rear end of the truck to spread the material on the road under treatment.
In the known apparatus of this type the conveyor normally takes the form of an endless flexible belt placed in a substantially horizontal position. This belt needs to be driven by powerful motors. Furthermore it has to be particularly strong in order to handle the significant loads to which it is subjected.
There is also known apparatus of this type in which the conveyor comprises an endless screw or the like having a substantially horizontal axis. Here again the apparatus requires powerful driving means in order to achieve the rotation of the endless screw.
In every case the conveyor has to be particularly strongly built in order to work in a particular environment.
The invention has in particular the aim of providing a solution to the above problems.
According to the invention, apparatus for spreading a granular material comprises at least one conveyor designed to move the material from a hopper to a distributor, the conveyor comprising two endless cables mounted in parallel and each passing around two end pulleys, transverse parallel bars each secured to the cables at regular intervals and designed to move the material along a transport surface, and driving means designed to move the cables in synchronism.
Thus the conveyor according to the invention comprises essentially parallel bars driven by endless cables and moving the material from the hopper to the distributor. It is thus the cables and the bars that handle the high mechanical forces of the conveyor. They can be made of a material having a high mechanical strength, for example stainless steel.
According to another feature of the invention the bars are fixed to the cables by attachment members designed to engage in recesses of appropriate shape provided on the periphery of at least one of the pulleys. Thus the pulleys act as toothed engaging means which ensure the driving of the cables by co-operation with the attachment members for the bars.
In one embodiment, each of the attachment members is a staple having two limbs joined together by a U-shaped hoop, while the above-mentioned recesses have a shape which is adapted to receive a respective hoop of an attachment member.
In another embodiment, each of the attachment members comprises a locking plate having a cylindrical pin, whilst the recesses have a shape adapted for receiving the respective pin of the attachment member.
The transport surface of the apparatus could be a substantially horizontal fixed surface above which the bars move. In this case these bars scrape along the transport surface in order to ensure the movement of the granular material.
This transport surface preferably constitutes the floor of the hopper and it extends as far as the distributor.
In another embodiment the bars and the cables are fixed to a continuous deformable conveyor belt which constitutes the transport surface. However, in this embodiment, the belt does not have to handle any forces since it is always the cables and the bars which provide the mechanical driving force.
In every case the hopper preferably has a wall provided with a calibrated opening past which the conveyor moves. The result is that it delivers a metered quantity of material depending on the cross-section of the calibrated opening and the linear speed of the conveyor.
The driving means preferably comprise at least one motor-driven spindle on which are secured two pulleys designed to drive the two cables in synchronism. Preferably each cable passes around a tension pulley.